1. Field of the Invention
The present invention relates to a recording layer determination apparatus for determining whether a recording layer is single-layer or multi-layer, a method for determining recording layer, a computer-readable recording medium having stored therein recording layer determination program to be executed on a computer, and a recording layer determination program to be executed on a computer, which are preferably provided for equipment capable of dealing with recording medium having respective constructions of the single-layer and multi-layer such as a video-game unit, a digital videodisc unit, a magnetic optical disc unit, or a magnetic disc unit.
2. Description of the Related Art
There is a conventionally known recording medium with two-dimensional structure where recording layer is “single-layer”, such as CD-ROM or so forth.
Further, there is a known recording medium (three-dimensional recording medium) with three-dimensional structure of “multi-layer” where a plurality of recording layers are laminated, such as DVD, FMD (Fluorescent Multi-layer Disc) or so forth, besides the recording medium with two-dimensional structure of “single-layer.”
Equipments for handling the recording medium with three-dimensional structure are required to ensure compatibility between the single-layer recording medium and the multi-layer recording medium. It is necessary to change setting of laser level, gain of each signal or so forth between the recording medium of the single-layer and the recording medium of the multi-layer for making it possible to operate both recording medium of the single-layer and the multi-layer Therefore, equipment capable of dealing with the three-dimensional recording medium determines whether the recording medium is the recording medium of the single-layer or the recording medium of the multi-layer before recording or reproducing. And then the equipment executes recording or reproducing with respect to the recording medium while changing setting of each unit on the basis of the determination result.
For example, in the case of a DVD unit capable of dealing with a DVD of the multi-layer, level determination system is adopted, where an optical pickup is brought near the DVD gradually from predetermined position to obtain difference of signal level of reproduce signal (sum−signal=RF signal) from the optical pickup, and then the DVD unit executes determination between the single-layer and the multi-layer or determination of phase change disc of DVD-RW and so forth based on the difference of signal level of the reproduce signal (sum−signal=RF signal) obtained from the optical pickup.
While, also in the case of the DVD unit capable of dealing with the DVD of the multi-layer, focus error count system is adopted, where an optical pickup is brought near the DVD gradually from predetermined position to obtain the number of error of focus error signal (FE signal) from the optical pickup, and then the DVD unit executes determination between the single-layer and the multi-layer based on counted value while counting the number of error of the focus error signal obtained from the optical pickup.
Specifically, in the above described level determination system, when the optical pickup is brought near the DVD gradually from the predetermined position with the optical pickup as constant laser level, the signal level of reproduce signal obtained from the optical pickup is a curved line as illustrated in FIG. 1 in the case of the DVD of the single-layer, while in the case of the DVD of the multi-layer the signal level of reproduce signal obtained from the optical pickup is a curved line as illustrated in FIG. 2.
Namely, as illustrated in FIG. 1 and FIG. 2, when the optical pickup is brought near the DVD gradually from the predetermined position (Disc Far→Disc Near), first, one reproduce signal (disc surface reflected signal) by reflected light from protection film of the disc made of polycarbonate resin is capable of being obtained, subsequently, the other reproduce signal (signal surface reflected signal) by reflected light from a recording layer (signal surface) is capable of being obtained.
As shown in FIG. 1 and FIG. 2, there is no level difference of the disc surface reflected signal between the single-layer (FIG. 1) and the multi-layer (FIG. 2). However, the signal surface reflected signal, in the case of the DVD of the single-layer, has one peak level corresponding to recording surface of the single-layer, further, the level itself is large on the other hand, in the case of the DVD of the multi-layer, the signal surface reflected signal of the multi-layer has a plurality of peak levels corresponding to a plurality of recording surfaces (in the case of example shown in FIG. 2, since the DVD comprises of two-layer, two peak levels exist). In addition, the peak level itself is low in comparison with the DVD of the single-layer caused by difference of transmittance of light of each layer or caused by diffused reflection of light because of existence of clearance gap between respective layers (reflection level P1>reflection level P2).
Therefore, in order to determine layer state, the level determination system sets a threshold value to be reference level between a peak level of a signal surface reflected signal obtained from the DVD of the single-layer and a peak level of a signal surface reflected signal obtained from the DVD of the multi-layer. And then the level determination system determines that is DVD is the DVD of the single-layer if the signal level of the signal surface reflected signal is the threshold value or more. While the level determination system determines that its DVD is the DVD of the multi-layer or its DVD is low reflection recording medium (phase change disc such as DVD-RW and so forth) if the signal level of the signal surface reflected signal is a signal level less than the threshold value.
Therefore, it is possible to execute determination between a single-layer low reflection recording medium and a multi-layer low reflection recording medium depending on difference of reflectance of each DVD of the low reflection recording medium of the single-layer or the low reflection recording medium of the multi-layer.
On the other hand, in the above described focus error count system, when the optical pickup is brought near the DVD gradually from the predetermined position with the optical pickup as constant laser level, in the case of the DVD of the single-layer, it is possible to obtain a focus error signal (FE) at backwards and forwards of the focus as illustrated in FIG. 3. In addition, in the case of the DVD of the multi-layer, it is possible to obtain a focus error signal at backwards and forwards of the focus a, illustrated in FIG. 4.
In the focus error count system, a threshold value for high level (FcmpH Slice Level) with respect to this focus error signal is set. According to this setting, the FcmpH signal to be a signal of high level is formed during the period where the value of the focus error signal is the threshold value for high level or more.
Alternatively, in the focus error count system, a threshold value for low level (FcmpL Slice Level) with respect to this focus error signal is set. According to this setting, the FcmpL signal to be a signal of high level is formed during the period where the focus error signal has value less than the threshold value for low level.
As indicated in the FcmpH signal or FcmpL signal shown in FIG. 3 and the FcmpH signal or the FcmpL signal shown in FIG. 4, in the case of the DVD of the single-layer, the number of pulse of the FcmpH signal or the FcmpL signal is one as shown in FIG. 3. However, in the case of the DVD of the multi-layer, the FcmpH signal or the FcmpL signal has plural number of pulses as shown in FIG. 4 (in the case of the example of FIG. 4, since the DVD is a DVD of two-layer, the FcmpH signal and the FcmpL signal have two pulses respectively.)
The focus error count system determines a DVD as a DVD of the single-layer if the number of pulse is one, while the focus error count system determines a DVD as a DVD of the multi-layer if the number of pulse is plural by counting the number of pulse. Therefore, the focus error count system is capable of determining whether recording layer of the DVD is a single-layer or a multi-layer.
However, the level determination system and the focus error count system to be the conventional determination system between the single-layer and the multi-layer have following problems, where, in the both systems, dependence on signal level of the reproduce signal or the focus error signal is large.
The level determination system is effective for judgment of setting of various kinds of gain at the time of recording and reproducing. However, there are problems that threshold value setting of optimum level is required in every equipment for determination between the single-layer and the multi-layer, or tolerance with respect to variation of reflectance of the media caused by secular change is narrow.
On the other hand, in the case of equipment of the focus error count system, because of the same reason as equipment of the level determination system, it is difficult to set the threshold value for high level (FcmpH Slice Level) or the threshold value for low level (FcmpL Slice Level) to optimum levels respectively, thus there is the problem that accurate pulse for counting is not formed.
In addition, in the case of the equipment of the focus error count system, there is the problem that it is not possible to execute counting the number of pulse accurately caused by generation of false pulse described below.
The focus error signal (FE) has, in some cases, undulation on its signal waveform at backwards and forwards of the focus caused by detecting method of the focus error, optical design of the optical pickup, temperature variation, signal gain and so forth as shown in FIG. 3 and FIG. 4. In cases where a level of the undulation becomes the threshold value for high level (FcmpH Slice Level) or more, or in a cases where a level of the undulation becomes a level less than the threshold value for low level (FcmpL Slice Level), false pulses, which are not generated primarily, are generated as illustrated by dotted line of pulse of waveform in FIG. 3 and FIG. 4.
In the case of the focus error count system, since determination between the single-layer and the multi-layer is executed by counting the number of pulse of the FcmpH signal or the FcmpL signal, if such false pulses are generated, the count value of the number of pulse of the FcmpH signal or the FcmpL signal becomes different count value from the original count value, it is not possible to execute accurate determination between the single-layer and the multi-layer.
For example, in the case of the DVD of the single-layer illustrated in FIG. 3, the count value of the number of pulse of the FcmpH signal or the FcmpL signal should originally be one. However, since dotted line waveform of false pulse is counted, counted value becomes two, although the DVD should be the DVD of the single-layer, the DVD is inadvertently determined as the DVD of the multi-layer.